System for detection of a ground fault in a high resistance ground network

ABSTRACT

A method is provided for detection of a ground fault in a high resistance network in a voltage source power conversion circuit comprising a power converter that converts incoming AC power to DC power applied to a DC bus and an inverter that converts DC power from the DC bus to output AC power. The method includes detecting a midpoint-to-ground voltage between a low side of the DC bus and a ground potential and detecting the presence of a ground fault in a high resistance network based upon the detected midpoint-to-ground voltage.

BACKGROUND

The invention relates generally to power conversion circuits and,particularly to a system for detection of a ground fault in a highresistance ground network system.

Wide ranges of equipment utilizing various power converter circuits areknown, such as electric motor drive systems used in factory automationsystems, power generation systems and so forth. Typically an electricmotor drive is connected to a power source, most often the power grid,and operates to provide electrical power to a load in a controlledmanner.

In voltage power conversion circuits, electrical power is converted froman AC power source into direct current (DC) power via a power converter.The DC power is then converted via an inverter coupled to the converterthrough a DC bus into AC power with controlled frequency, phase andamplitude, which may be applied to drive an external load such as theelectric motor.

Typically, it is desirable to detect whether a drive is operating in aground fault on a high resistance ground network so that the groundfault may be cleared before it causes failures in components of thecircuit. In operation, the bus voltages increase substantially during aground fault resulting in high voltage stresses in the components suchas motor and cables of the system. Because of the high resistance thatnormally exists during the ground faults on high resistance groundnetworks, the fault current is small and therefore often negligiblethereby making it difficult to reliably separate such faults from largechanges of the load.

Most conventional techniques for detecting ground faults on highresistance ground networks are based on simplified impedance models forthe transmission line. However, these techniques lack sufficientaccuracy when applied to systems containing power converters. Anotherway of detecting ground faults on high resistance ground networks is bymeasuring output phase to ground voltage in the circuit. However, suchtechnique is complicated and can identify only output phase to groundfault.

Accordingly, it would be desirable to develop a system that detectspresence and location of ground faults on high resistance groundnetworks in power conversion circuits during and/or prior to operationof such systems.

BRIEF DESCRIPTION

Briefly, according to one embodiment of the present invention, a methodis provided for detection of a ground fault in a high resistance groundnetwork in a voltage source power conversion circuit comprising a powerconverter that converts incoming AC power to DC power and an inverterthat converts the DC power to output AC power. The method includesdetecting a midpoint-to ground voltage between a low side of the DC busand a ground potential and detecting the presence of a ground fault in ahigh resistance network based upon the detected midpoint-to-groundvoltage.

In accordance with another aspect, a system is provided for detection ofground fault in high resistance network. The system includes anamplifier configured to be coupled to a side of a DC bus to detect avoltage at a node between the midpoint of the DC bus and a groundpotential. The system also includes a low pass filter coupled to anoutput of the amplifier to generate a midpoint-to-ground signal

In accordance with another aspect, a system is provided for detection ofa ground fault in a high resistance ground network. The system includesa voltage source power conversion circuit comprising a power converterthat converts incoming AC power to DC power applied to a DC bus and aninverter that converts DC power from the DC bus to output AC power. Thesystem also includes a midpoint-to-ground voltage detection circuitcoupled to a low side of the DC bus and to a ground potential andconfigured to generate a midpoint-to-ground voltage signal and amonitoring and analysis circuit coupled to the midpoint-to-groundvoltage detection circuit and configured to detect a ground fault in ahigh resistance network based upon the midpoint-to-ground voltagesignal.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an exemplary voltage power conversion circuit with asystem for detecting a ground fault in a high resistance network inaccordance with aspects of the present invention.

FIG. 2 illustrates an exemplary configuration of a DC bus voltagemeasurement circuit with a midpoint-to-ground voltage detection circuitemployed in the voltage power conversion circuit of FIG. 1.

FIG. 3 illustrates exemplary process steps for detecting a highresistance fault in the voltage source power conversion circuit of FIG.1 prior to powering a load of the circuit or removal of the load of thecircuit.

FIG. 4 illustrates exemplary process steps for detecting a highresistance fault in the voltage source power conversion circuit of FIG.1 during powering a load of the circuit.

FIG. 5 illustrates exemplary process steps for detecting a location of aload side ground fault in a high resistance network using the outputfrequency component (V_(mgload)) of the midpoint-to-ground voltageestimated using the process of FIG. 4.

FIG. 6 illustrates another exemplary embodiment of detecting DC groundfault using the measured midpoint-to-ground voltage.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present techniquefunction to provide a system for detection of a ground fault in a highresistance ground network in a power conversion circuit such as employedin motor drive systems. In particular, the present technique providesoff-line and on-line detection techniques to detect presence andlocation of the ground fault (such as load side, DC side or AC inputside) based upon a measured midpoint-to-ground voltage.

References in the specification to “one embodiment”, “an embodiment”,“an exemplary embodiment”, indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Turning now to drawings and referring first to FIG. 1, a voltage powerconversion circuit 10 is illustrated. The voltage power conversioncircuit 10 includes a power converter 12 configured to receive incomingAC power from a power source 14 and to convert the AC power to DC powerapplied to a DC bus 16. The voltage power conversion circuit 10 alsoincludes an inverter 18 coupled to the power converter 12 that convertsDC power from the DC bus 16 to output AC power. Further, a motor 20 iscoupled to and driven by the inverter 18. In the illustrated embodiment,the voltage power conversion circuit 10 further includes a load 22coupled to and driven by the motor 20.

In the illustrated embodiment, the voltage power conversion circuit 10includes filter circuitry 24 for filtering higher order harmonics fromAC power received from the power source 14. In certain embodiments, thefilter circuitry 24 includes an electromagnetic interference andharmonic filter. Further, the voltage power conversion circuit 10includes bus capacitor and filter 26 configured to filter harmonicsassociated with the DC bus 16.

In the illustrated embodiment, the voltage power conversion circuit 10further includes a DC bus voltage measurement circuit 28 configured tomeasure the DC bus voltage. Moreover, a midpoint-to-ground voltagedetection circuit 30 is coupled to the DC bus voltage measurementcircuit 28. In a presently contemplated configuration, themidpoint-to-ground voltage detection circuit 30 is coupled to a midpointof the DC bus 16 and to a ground potential and is configured to generatea midpoint-to-ground voltage signal. The voltage power conversioncircuit 10 also includes a monitoring and analysis circuit 32 coupled tothe midpoint-to-ground voltage detection circuit 30 and configured todetect a ground fault in a high resistance network based upon themidpoint-to-ground voltage signal.

It should be noted that, while the present techniques for detectingground fault in high resistance ground network are described inconnection with a motor drive, the techniques are not limited to suchapplications. Rather, the same methodology may be utilized for detectingground faults in a wide range of circuit applications, particularlythose in which a DC bus is used in conjunction with AC/DC rectification,or more generally conversion circuitry, and DC/AC conversion circuitry.

In one embodiment, the monitoring and analysis circuit 32 is configuredto detect the ground fault in a high resistance network prior toapplying the power to the load 22. In operation, the monitoring andanalysis circuit 32 is configured to determine whether the detectedmidpoint-to-ground voltage exhibits a line side fundamental frequencycomponent indicative of a line side ground fault. In another exemplaryembodiment, the monitoring and analysis circuit 32 is configured todetermine whether the detected midpoint-to-ground voltage exhibits a DCoffset component indicative of a DC bus ground fault.

In another exemplary embodiment, the monitoring and analysis circuit 32is configured to determine whether the detected midpoint-to-groundvoltage exhibits a DC offset component while placing all high sideswitches or low side power electronic switches of the inverter 18 into aconducting state. In this exemplary embodiment, the voltage powerconversion circuit 10 includes a control circuit 34 and a driver circuit36 for controlling operation of the power electronic switches of theinverter 18.

In another exemplary embodiment, the monitoring and analysis circuit 32is configured to detect the ground fault in a high resistance networkduring driving of the load 22 with the output AC power. In thisexemplary embodiment, the monitoring and analysis circuit 32 isconfigured to detect a line side fundamental frequency component of themidpoint-to-ground voltage indicative of a line side ground fault.Moreover, the monitoring and analysis circuit 32 is configured to detecta DC offset component of the midpoint-to-ground voltage indicative of aDC bus ground fault. In addition, the monitoring and analysis circuit 32is configured to detect an output frequency component of themidpoint-to-ground voltage indicative of a load side ground fault.

In the illustrated embodiment, monitoring and analysis circuit 32includes a memory 38 configured to store the detected midpoint-to-groundvoltage. Further, the monitoring and analysis circuit 32 also includes aprocessor 40 configured to determine components such as line sidefundamental frequency component of the midpoint-to-ground voltagesignal, DC offset component of the midpoint-to-ground voltage signal andoutput frequency component of the midpoint-to-ground voltage signal todetect the line side ground fault, the DC bus ground fault and the loadside ground fault respectively.

The memory 38 may include hard disk drives, optical drives, tape drives,random access memory (RAM), read-only memory (ROM), programmableread-only memory (PROM), redundant arrays of independent disks (RAID),flash memory, magneto-optical memory, holographic memory, bubble memory,magnetic drum, memory stick, Mylar® tape, smartdisk, thin film memory,zip drive, and so forth. In certain embodiments, the information aboutthe detected ground fault in a high resistance network may be displayedto a user through a display 42.

It should be noted that the present invention is not limited to anyparticular processor for performing the processing tasks of theinvention. The term “processor,” as that term is used herein, isintended to denote any machine capable of performing the calculations,or computations, necessary to perform the tasks of the invention. Theterm “processor” is intended to denote any machine that is capable ofaccepting a structured input and of processing the input in accordancewith prescribed rules to produce an output. It should also be noted thatthe phrase “configured to” as used herein means that the processor isequipped with a combination of hardware and software for performing thetasks of the invention, as will be understood by those skilled in theart.

FIG. 2 illustrates an exemplary configuration 50 of the DC bus voltagemeasurement circuit 28 with the midpoint-to-ground voltage detectioncircuit 30 employed in the voltage power conversion circuit 10 ofFIG. 1. In the presently contemplated configuration, themidpoint-to-ground voltage detection circuit 30 includes an amplifier 52coupled to a low side 54 of the DC bus 16 to detect a voltage at a nodebetween the low side 54 of the DC bus 16 and a ground potential 56.Moreover, a low pass filter 58 is coupled to an output of the amplifier52 to generate a midpoint-to-ground voltage signal 60. In this exemplaryembodiment, the low pass filter 58 is configured to filter switchingripples in the detected voltage and generate the midpoint-to-groundvoltage signal 60.

As described before with reference to FIG. 1, the midpoint-to-groundvoltage signal 60 is processed by the monitoring and analysis circuit 32to detect the presence and location of the ground fault. In particular,the midpoint-to-ground voltage signal 60 is analyzed to determine lineside fundamental frequency component of the midpoint-to-ground voltagesignal 60, DC offset component of the midpoint-to-ground voltage signal60 and output frequency component of the midpoint-to-ground voltagesignal 60 to detect line side ground fault, DC bus ground fault and loadside ground fault. It should be noted that the presence and location ofthe ground fault may be detected prior to or during driving of the load22 with the output AC power that will be described in a greater detailbelow.

FIG. 3 illustrates exemplary process steps 70 for detecting a highresistance fault in the voltage source power conversion circuit 10 ofFIG. 1 prior to powering the load 22. At block 72, a ground fault checkis initialized. In this exemplary embodiment, the inverter of thevoltage source power conversion circuit is not operating and the load isnot powered. At block 74, initial source grounding type is determinedfor the circuit 10. In certain embodiments, the initial source groundingmay be specified by a user of the voltage source power conversioncircuit 10.

If the circuit is identified as a Y grounded system, then it isdetermined if the midpoint-to-ground voltage exhibits a fundamentalfrequency component (block 76). In this exemplary embodiment, it isverified if the fundamental frequency of the midpoint-to-ground voltageis about 60 Hz (in North America). Further, if the detected fundamentalfrequency component of the midpoint-to-ground voltage is substantiallysame as of the input phase voltage, the fault is characterized as asource side ground fault (block 78).

Moreover, if the fundamental frequency component of themidpoint-to-ground voltage is different from the input phase voltage,then it is determined if the midpoint-to-ground voltage exhibits a DCoffset component (block 80). In certain embodiments, the DC offsetcomponent of the midpoint-to-ground voltage is further determined for acorner grounded system (block 82). The DC offset component of themidpoint-to-ground voltage is compared with a pre-determined thresholdto detect a DC bus ground fault, as represented by block 84.

In one exemplary embodiment, the DC offset component of themidpoint-to-ground voltage is approximated by the following equation:

V _(ng) _(—dc) ½×V _(dc) ×R _(gnd)/(R _(gnd) +R _(flt))  (1)

where: V_(mgdc) is the DC offset component of the midpoint-to-groundvoltage, Vdc is the measured differential DC bus voltage, Rgnd is theneutral resistance, and Rflt is the ground fault resistance.

If the DC offset component of the midpoint-to-ground voltage has asubstantially low value, then all high side or low side power electronicswitches of the inverter are placed into a conducting state, asrepresented by block 86. Again, at block 88, the DC offset component ofthe midpoint-to-ground voltage is verified. In one exemplary embodiment,when all the power electronic switches are disabled, themidpoint-to-ground voltage does not exhibit a DC offset component.

If the DC offset component of the midpoint-to-ground voltage is higherthan a pre-determined threshold then a load side ground fault isidentified (block 90). Moreover, current components are checked, asrepresented by block 92, to detect which phase of the load is faulted.In this embodiment, the output load currents are represented by I_(su),I_(sv), and I_(sw) respectively. For example, in the illustratedembodiment, the current component is substantially high in phase “x”indicative of a load side ground fault in phase “x” (block 94).

In another embodiment, if the value of the DC offset component of themidpoint-to-ground voltage is lower than the pre-determined threshold,it indicates a no fault condition (block 96). The high side or the lowside power electronic switches are then placed in their respective nonconducting state and the ground fault status is reported with the systembeing ready for next cycle, as represented by block 98.

FIG. 4 illustrates exemplary process steps 110 for detecting a highresistance fault in the voltage source power conversion circuit 10 ofFIG. 1 during driving the load 22. At block 112, switching ripples arefiltered from measured a midpoint-to-ground voltage (V_(mg)). Further, aband pass filter is employed to detect a line side fundamental frequencycomponent (V_(mgs)) of the midpoint-to-ground voltage (block 114). Inthis exemplary embodiment, the initial source grounding type isdetermined for the circuit 10 prior to measuring the midpoint-to-groundvoltage. At block 116, the line side fundamental frequency component iscompared with a first threshold. In this exemplary embodiment, the firstthreshold is a function of the source voltage (V_(s)) of the AC inputand a first constant (k1). In certain exemplary embodiments, the firstconstant k1 is about 0.25 to about 0.75. In one exemplary embodiment,the first constant k1 is about 0.5.

If the line side fundamental frequency component is greater than thefirst threshold, then the system has a line side ground fault on a Y orcorner grounded system (block 118). Alternatively, if the line sidefundamental frequency component is lesser than the first threshold, thenthe system does not have a line side ground fault (block 120).

In this exemplary embodiment, another band pass filter with filteringfrequency as the inverter frequency is employed to determine an outputfrequency component (V_(mgload)) (block 122). Furthermore, at block 124,the output frequency component is compared with a second threshold. Inthis exemplary embodiment, the second threshold is a function of theoutput voltage (V_(o)) and a second constant (k2). In certain exemplaryembodiments, the second constant is about 0.25 to about 0.75. In oneexemplary embodiment, the second constant k2 is about 0.5.

If the output frequency component is greater than the second threshold,then the system has a load side ground fault (block 126). Alternatively,if the output frequency component is lesser than the second threshold,then the system does not have a load side ground fault (block 128).

In this exemplary embodiment, the DC offset component (V_(mgdc)) of themidpoint-to-ground voltage is determined, as represented by block 130.At block 132, the DC offset component is compared with a thirdthreshold. In this exemplary embodiment, the third threshold is afunction of the bus voltage (V_(dc)) and a third constant (k3). Incertain exemplary embodiments, the third constant is about 0.25 to about0.75. In one exemplary embodiment, the third constant is about 0.5.

If the DC offset component is greater than the third threshold, then thesystem has a DC bus ground fault (block 134). Alternatively, if the DCoffset component is lesser than the third threshold, then the systemdoes not have a DC bus ground fault (block 136).

FIG. 5 illustrates exemplary process steps 140 for detecting a locationof a load side ground fault in a high resistance network using theoutput frequency component (V_(mgload)) of the midpoint-to-groundvoltage estimated using the process of FIG. 4. As illustrated, the loadside ground fault is detected using the output frequency component ofthe midpoint-to-ground voltage (block 126). At block 142, a phase angle(∠V_(mgload)) of the output frequency component of themidpoint-to-ground voltage is estimated. Furthermore, the estimatedphase angle is combined with a phase angle (∠V_(o)) of the inverteroutput voltage to determine a differential phase angle (φ) (block 144).

At block 146, it is verified if the differential phase angle is aconstant value. If the differential phase angle does not have a constantvalue, then it is indicative of load side ground fault for another driveof the system. Alternatively, if the differential phase angle exhibits aconstant value, then the output frequency component of themidpoint-to-ground voltage is utilized to determine a respective phaseangle for each phase of the drive indicative of the fault in therespective phase of the drive (blocks 152 and 154). In this exemplaryembodiment, the phase angle is indicative of phase “x” of the drivebeing ground faulted.

FIG. 6 illustrates another exemplary embodiment 160 of detecting DCground fault using the measured midpoint-to-ground voltage. In thisexemplary embodiment, the midpoint-to-ground voltage (V_(mg)) signalobtained using the midpoint-to-ground voltage detection circuit of FIG.1 is filtered to filter out switching ripples and DC signals (block162). Further, a root mean square value is estimated to determine themagnitude of the fundamental frequency component (V_(mgs)) of themidpoint-to-ground voltage (block 164). Similarly, themidpoint-to-ground voltage (V_(mg)) signal is filtered to filter outswitching ripples and DC signals to determine the magnitude of the DCoffset component (V_(mgdc)) of the midpoint-to-ground voltage.

In one exemplary embodiment, if the fundamental frequency component(V_(mgs)) is greater than a pre-determined threshold, then an AC groundfault signal is displayed. In another exemplary embodiment, if the DCoffset component (V_(mgdc)) is greater than a pre-determined threshold,then a DC ground fault signal is displayed. Thus, this techniquefacilitates online detection of the AC and DC ground faults using thefundamental frequency component and the DC offset component of themidpoint-to-ground voltage.

As will be appreciated by those of ordinary skill in the art, theforegoing example, demonstrations, and process steps may be implementedby suitable code on a processor-based system, such as a general-purposeor special-purpose computer. It should also be noted that differentimplementations of the present technique may perform some or all of thesteps described herein in different orders or substantiallyconcurrently, that is, in parallel. Furthermore, the functions may beimplemented in a variety of programming languages, such as C++ or JAVA.

Such code, as will be appreciated by those of ordinary skill in the art,may be stored or adapted for storage on one or more tangible, machinereadable media, such as on memory chips, local or remote hard disks,optical disks (e.g., CD's or DVD's), or other media, which may beaccessed by a processor-based system to execute the stored code. Notethat the tangible media may comprise paper or another suitable mediumupon which the instructions are printed. For instance, the instructionscan be electronically captured via optical scanning of the paper orother medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory.

The various aspects of the structures described hereinabove may be usedfor detecting ground faults in high resistance ground systems such asmotor drive systems. In particular, the technique described aboveutilizes a midpoint-to-ground voltage signal for detecting the presenceand location of the ground fault in high resistance network.Advantageously, the technique facilitates offline and onlineidentification of the ground fault in a high resistance network at thedrive load side, DC bus side and the line side thereby enhancing thereliability of such systems.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method for detection of a ground fault in high resistance groundsystem, comprising: in a voltage source power conversion circuitcomprising a power converter that converts incoming AC power to DC powerapplied to a DC bus and an inverter that converts DC power from the DCbus to output AC power, detecting a midpoint-to-ground voltage between alow side of the DC bus and a ground potential; and; detecting thepresence of a ground fault in a high resistance network based upon thedetected midpoint-to-ground voltage.
 2. The method of claim 1,comprising detecting the location of the ground fault in the powerconversion circuit.
 3. The method of claim 2, wherein the presence andlocation of the ground fault in the high resistance system are detectedprior to powering a load with the output AC power.
 4. The method ofclaim 3, comprising determining whether the detected midpoint-to-groundvoltage exhibits a DC offset component indicative of a DC bus groundfault.
 5. The method of claim 3, comprising determining whether thedetected midpoint-to-ground voltage exhibits a line side fundamentalfrequency component indicative of a line side ground fault.
 6. Themethod of claim 3, comprising placing all high side or low side powerelectronic switches of the inverter into a conducting state anddetermining whether the detected midpoint-to-ground voltage exhibits aDC offset component indicative of a load side ground fault.
 7. Themethod of claim 1, wherein the presence and location of the ground faultin the high resistance system are detected during powering a load withthe output AC power.
 8. The method of claim 7, comprising comparing aline side fundamental frequency component of the detectedmidpoint-to-ground voltage with a first threshold to detect a line sideground fault, wherein the first threshold is a function of a sourcevoltage of the AC input power.
 9. The method of claim 7, comprisingcomparing an output frequency component of the detectedmidpoint-to-ground voltage during powering of the load with a secondthreshold to detect a load side ground fault, wherein the secondthreshold is a function of an output voltage.
 10. The method of claim 8,comprising estimating phase angles of the detected midpoint-to-groundand the output voltages respective to determine the location of the loadside ground fault.
 11. The method of claim 7, comprising comparing a DCoffset component of the midpoint-to-ground voltage with a thirdthreshold to detect a DC bus ground fault, wherein the third thresholdis a function of the bus voltage.
 12. The method of claim 7, comprisingdetermining the fundamental frequency component and a DC offsetcomponent of the midpoint-to-ground voltage indicative of the AC or DCground fault.
 13. A system for detection of ground fault in highresistance ground network, comprising: an amplifier configured to becoupled to a low side of a DC bus to detect a voltage at a node betweenthe low side of the DC bus and a ground potential; and a low pass filtercoupled to an output of the amplifier to generate a midpoint-to-groundsignal.
 14. The system of claim 13, further comprising a monitoring andanalysis circuit configured to detect a ground fault in the highresistance network based upon the midpoint-to-ground signal.
 15. Thesystem of claim 14, wherein the monitoring and analysis circuit isconfigured to detect a location of the ground fault in the highresistance network based upon the midpoint-to-ground signal.
 16. Thesystem of claim 15, wherein the monitoring and analysis circuit isconfigured to detect a DC bus ground fault, a load side ground fault,and a line side ground fault based upon a DC offset component of themidpoint-to-ground signal and a fundamental frequency component of themidpoint-to-ground signal.
 17. A system for detection of ground fault ina high resistance ground network, comprising: a voltage source powerconversion circuit comprising a power converter that converts incomingAC power to DC power applied to a DC bus and an inverter that convertsDC power from the DC bus to output AC power; a midpoint-to-groundvoltage detection circuit coupled to a low side of the DC bus and to aground potential and configured to generate a midpoint-to-ground voltagesignal; and a monitoring and analysis circuit coupled to themidpoint-to-ground voltage detection circuit and configured to detect aground fault in a high resistance network based upon themidpoint-to-ground voltage signal.
 18. The system of claim 17, whereinthe midpoint-to-ground voltage detection circuit is coupled to a DC busvoltage measurement circuit.
 19. The system of claim 18, wherein themidpoint-to-ground voltage detection circuit comprises an amplifiercoupled to the low side of the DC bus to detect a voltage at a nodebetween the low side of the DC bus and a ground potential, and a lowpass filter coupled to an output of the amplifier to generate themidpoint-to-ground voltage signal.
 20. The system of claim 17, whereinthe monitoring and analysis circuit is configured to detect the groundfault in the high resistance network prior to and during powering a loadwith the output AC power.
 21. The system of claim 20, wherein themonitoring and analysis circuit is configured to detect a location ofthe ground fault in the high resistance network based upon a DC offsetcomponent and a frequency component of the neutral to ground voltagesignal.
 22. The system of claim 21, wherein the monitoring and analysiscircuit is configured to estimate a phase angle of the neutral to groundvoltage to detect a phase of the drive with the ground fault in a highresistance ground system.